Optical communication systems transport information in the form of modulated light signals. A laser module, e.g. a semiconductor laser (laser=light amplification by stimulated emission of radiation) in a signal transmitter unit is here normally used in order to accomplish the optical signals on basis of electrical ditto, and a photodetection module, e.g. a photodiode, in a signal receiver unit typically converts the optical signals back into electrical signals again. In most cases, the signal transmitter unit and a corresponding signal receiver unit are co-located to form an optoelectrical transceiver unit.
The above transmitter and receiver units should generally be as small as possible with the aim of concentrating the number of processed information bits per physical volume unit and thereby reduce the overall size of the optical communication equipment. For the same reason, the units should also be placed as close as possible to each other.
Traditionally, the transmitter and receiver units are placed in a respective indentation in the circuit board. Furthermore, the units are usually oriented with their largest side in parallel with the circuit board, such that they show a largest possible interface area towards a heat sink below and/or above the circuit board. This design, however, places a theoretical lower limit as to the circuit board area required to house a certain number of units, which basically is proportional to the area of the largest unit sides. Moreover, the assembly of such a transceiver becomes relatively complex, particularly if the units are positioned very close to each other.
The document WO01/42840 discloses a modular fiber-optic transceiver, which includes a sub-assembly stack mounted with its largest sides oriented perpendicular to the circuit board. Thereby, it appears possible to place rather many sub-assembly stacks per area unit on the circuit board. Specifically, the document proposes a first design where a standard single solder pin array connects the sub-assembly to the transceiver board. This design limits the data rate of the signals that are fed to or from the sub-assembly to a relatively low value, such that the design may only be used for low capacity optical processing modules. According to a second proposed design, a so-called flexible cable band instead attaches the sub-assembly to the transceiver board. Thereby, a higher data rate is enabled. However, the signal shielding is still inadequate and the mounting of the optoelectrical components becomes very complicated. Moreover, the flexible cable band approach severely limits the potential areas in which the sub-assembly may be positioned on the transmitter board.